Quick tune helical antenna



A ril 8, 1969 G. H. MENHENNETT QUICK TUNE HELICAL ANTENNA Filed June 17, 1966' (PR/0,? ART) 1! TTORNEY United States Patent US. Cl. 343-895 6 Claims ABSTRACT OF THE DISCLOSURE A tunable helical antenna characterized by helical sections arranged one upon the other and having a plurality of shorting brush assemblies, one assembly for each helical section, for shorting out selected turns of each of the antenna sections. A conductor connected to an end of each section and to a sliding contact on each of said assemblies provides the short. A common shaft drives all the assemblies simultaneously. Wheels forming part of each of the assemblies and restrained to ride along the inside of the helix cause the said assemblies which are mounted on the shaft, to slide along its axis when the shaft is rotated.

This invention relates to antenna tuning apparatus and more particularly to apparatus for rapidly tuning a helical antenna.

In certain communication applications it is required to tune an antenna over a frequency range in a very short time period; for example, an aircraft in communication with more than one party over more than one channel requires the capability to tune its antenna to the different channel frequencies with a minimum time lapse.

Accordingly, it is an object of this invention to provide an improved rapidly tunable antenna.

The abovementioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a conventional helical antenna employing conventional tuning; and

FIGURE 2 is an embodiment of a rapidly tunable antenna according to the invention.

Briefly, the embodiment illustrated provides a helical antenna comprising helical sections arranged one upon the other and having a plurality of shorting assemblies, one shorting assembly for each helical section, for shorting out selected ones of the turns of each of the antenna sections.

Referring to FIGURE 1, there is illustrated a conventional helical antenna comprising a helix 10 arranged about a rod 11 which is made of a nonmetallic material. Rod 11 is shown as having a triangular cross section but could have a square cross section or various other cross sections. Arranged for rotation within helix 10 is a shorting brush assembly 12 which includes shorting contacts 13, for contacting the turns of helix 10 and wheels 14 for traversing the helix 10 when shorting brush assembly 12 is rotated. Shorting assembly 12 has a triangular channel running through the center of it for mating with rod 11 such that when rod 11 is rotated (the rotating drive means not shown) it will cause shorting assembly 12 to go up or down the helix depending upon Whether the rod is rotated clockwise or counter-clockwise. When rod 11 is rotated the shorting brush assembly is rotated therewith and is caused to slide along the length of the rod 11 by grooved wheels 14 which are restrained to move along the helix 10.

For a conventional helical antenna of the type illustrated in FIGURE 1 containing turns it has been found that the tuning time is approximately 2 minutes. This tuning time is much greater than the permissible tuning time for many applications; for example, in one particular application it had been found necessary to tune a helical antenna in a time period of three seconds or less over a frequency range of 230 megacycles.

Referring to FIGURE 2, there is illustrated an embodiment of an antenna according to the invention comprising a plurality of helical sections 15 arranged about a rod 11, sections 15 being joined together by joints 16 to form the helical antenna. Associated with each helical section 15 is a shorting assembly 12 as described hereinbefore with reference to FIGURE 1. A conductor is connected at one end to joint 16 and at the other end to the shorting contact 13. The conductor 17 shorts out a predetermined number of turns which are determined by the location of the shorting assembly 12. In the embodiment, at the end section of the antenna, a conductor 17 is connected at one end to the shorting contact 13 and at the other end to a terminal 18 which is coupled to the end of the helix 15 by an antenna loading assembly which for simplicity is not shown. The connection thus provided is effectively a short circuit between these two points. Employing a helical antenna such as illustrated in FIGURE 2, but having 40 helical sections of 4 turns each it would be possible to tune the antenna in three seconds using the same motor speed where it required two minutes for a helix of 160 turns employing only a single shorting assembly. It should be noted that the entire helix can be tuned (changed from all open turn sections to all shorted sections) by 4 revolutions of the drive motor (not shown).

The sectionalizing of the helix assembly also has merit in that a less rigid mounting structure is required in the external radome as a slight movement between sections can be tolerated.

It would also be possible to vary the winding pitch or spacing between turns of different helical sections to allow the spacing to follow the voltage distribution required in the completed helical antenna. The only requirement is that all sections have the same number of turns.

The helical sections under most ideal conditions can be made identical and connected by a quick disconnect method so that mass production techniques may be used in addition to the easy replacement of one or more defective sections.

I claim:

1 A rapidly tunable antenna, comprising:

a helical antenna having a plurality of turns;

a plurality of shorting means each disposed to traverse different predetermined portions of said helical antenna for shorting out selected ones of said turns of said predetermined portions; and

a rotatable rod mating with each of said shorting means for causing said shorting means to simultaneously traverse said predetermined portions.

2. A rapidly tunable antenna as in claim 1 in which each of said shorting means is disposed to traverse the same number of turns of said antenna.

3. A rapidly tunable antenna as in claim 1 in which said helical antenna includes a plurality of individual helical sections each having its own shorting means.

4. A rapidly tunable antenna as in claim 3 in which said individual helical sections have different winding pitches.

'5. A rapidly tunable antenna as in claim 1 in which said plurality of shorting means are ganged to operate 5 unitedly.

6. A rapidly tunable antenna as in claim 1 wherein said helical antenna is arranged about said rod.

'4 References Cited UNITED STATES PATENTS 2,948,894 -8/ 1960 Carpenter 343-895 2,993,204- 7/1961 Macalpine 343895 3,179,941 4/ 1965 Harris et al 343895 ELI LIEB'ERMAN, Primary Examiner. 

